A general challenge related to wind turbines is when wind turbines are coupled to weak utility grids. A coupling to a weak grid may under some circumstances result in transfer of, e.g., transients, noise or voltage drops or peaks between the utility grid and a wind turbine coupled to the grid.
Testing the individual parts of a wind turbine system for the capability of complying with different grid conditions before the wind turbine system is shipped from the factory—often to very distant parts of the world—is, therefore, essential.
It is, however, not sufficient to make sure, that the electrical parts of the wind turbine system, such as the generator and the power frequency converter, are able to manage simulated grid conditions corresponding to what could be expected during operation of the wind turbine when they are tested as stand-alone units. This is due to the fact that the varying rotation speed of the drive train axis and the mechanical and electrical interactions between the different parts of the wind turbine nacelle have an important influence on the performance of the wind turbine system.
It is one of several objects of the invention to establish a system which is able to physically simulate a coupling between a wind turbine system and a grid or parts of a wind turbine system and a grid.